There are no stunning features in 9.1 and that's because it is an alignment release. This means that they are focused on making sure the Revit platform (all three versions) is coordinated well. Naturally improving overall performance and scalability is an ongoing task but unfortunately they are features that only a programmer's mother could love and appreciate 8-).
They also try very hard to tuck in other improvements that don't require as much development time/resources as those that ultimately appear in full "point oh" releases, like the next version Revit Building 10.0, release date tba.
Some of the things we really want Revit to do require considerable effort and even revisiting some of the decisions that were made several years ago. As anyone who has revisited design decisions on projects that take several years to develop can attest, this can be a daunting task. Now where did I put that drawing...?
So what do I really like this time out? I really appreciate the subtle parameter added to elevation view's, "Hide at scales coarser than". The same parameter that Sections have, this means you can specify an elevation's annotation should not appear in a scale that is coarser than the one you place it in or some other scale you choose. This will go part way to making it easier to manage these buggers in our projects. Still a way to go to make them really sing but a nice touch, THANKS!
A few more to keep this post short...
Units can be defined when exporting to dwg. For those working with the metric system it proved somewhat bothersome to find that the unit assigned was millimeter and that you now had to change it after exporting. Now you can specify it before hand. Muy Bueno, no?
Section lines are now better able to snap to non-orthogonal walls. Again a subtle but appreciated touch.
Now you can tell Columns that they are room bounding before you place them.
Revision clouds and their tags can now display separately as is the norm in many firms. As is their habit, once a new revision is made earlier clouds are turned off and the little delta tags remain. Until this release you couldn't keep the tags without the clouds, aaah...much better now.
Last one for now...filled regions have an area parameter. This permits you to sketch a filled region arbitrarily, in a view, and find out the area of the filled region by looking at its properties dialog. Since this is meant as a "throwaway" value it is not possible to schedule or tag, both of which would be nice to be able to do. Still...some users are wishing for a simple "pick based" area command like that of AutoCAD.